Catalytic fluid heater

ABSTRACT

A catalytic fluid heater having a housing in which is contained a copper tube which is formed into a series of concentric helical coils, and a number of perforated aluminum plates that are supported by the coils in various symmetric locations along the vertical axis of the copper tube. The underside of the plates are coated wtih a catalyst for combusting hydrogen, reformed natural gas, or low carbon monoxide content manufactured gas. The fluid to be heated flows through the copper tubing.

United States Patent 1191 Sharer et al. Oct. 7, 1975 [54] CATALYTIC FLUID HEATER 2,856,905 10/1958 Bowen 122/4 D 2, l D l l. 2 2 [75] Inventors Evanston; Jon 22373: 251332 125 /35 3 1? Pangborn, Lisle; Raymond J. Dufour Wheaten all of Primary Examiner-Kenneth W. Sprague [73] Assignee: Institute of Gas Technology, Assistant Examiner-Larry l. Schwartz Chicago, Ill. Attorney, Agent, or Firm-Dominik, Knechtel, Godula 22 Filed: Feb. 15, 1974 [21] Appl. No: 442,793 [57] ABSTRACT 52 US. Cl 126/350 R; 122/4 D; 122/250 R A catfilytc heater havfng f" [51] Int Cl 2 F24H 1/00 contalned a copper tube whlch 15 formed mto a serles of concentric helical coils, and a number of perforated [58] Fleld of Search 122/25 D; 110/97 D; l l t th t t d b th 23/288 F 431/l71 126/361 350R aummumpa es a aresuppore y eco1 s1nvarlous symmetrlc locat1ons along the vertlcal mm of the copper tube. The underside of the plates are coated [56] References Cited wtih a catalyst for combusting hydrogen, reformed UNITED STATES PATENTS natural gas, or low carbon monoxide content manul,642,539 9/1927 Choinski 122/155 A factured gas. The fluid to be heated flows through the 1,979,008 10/1934 MOITOW 126/350 R opper tubing 2,469,135 5/1949 Stone 126/350 R 2,778,610 1/1957 Bruegger 122/4 D 4 Claims, 3 Drawing Figures COLD WATER HOT F WATER H 7 1 U.S. Patent Oct. 7,1975

CATALYTIC FLUID HEATER This invention relates to an improved catalytic fluid heater. More particularly, it relates to an improved catalytic fluid heater which does not require external venting, or the use of electrical energy.

Conventional gas fired fluid heaters, particularly home water heaters, normally require external venting and hence special chimney constructions which add materially to building costs. The catalytic fluid heater of the present invention, although gas fueled, is fueled with hydrogen or other gases which are rich in hydrogen such as reformed natural gas and manufactured gas, in a fashion such that no venting is required because the combustion products are innocuous. In fact, the combustion products of the catalytic fluid heater is steam which can be utilized either to humidify a building or condensed to produce a distilled quality water. The catalytic fluid heater further is self-igniting and hence requires no standing pilots and need not consume fuel gas during periods of nil heat demand. The catalytic reaction is self-starting so that the heat or temperature sensing device need only be linked to the fuel gas supply valve to operate the latter to supply fuel to it Accordingly, it is an object of the present invention to provide an improved catalytic fluid heater.

More particularly, it is an object to provide an improved catalytic fluid heater which combusts hydrogen or other gases which are rich in hydrogen such as reformed natural gas and manufactured gas.

More particularly still, it is an object to provide an improved catalytic fluid heater which, although gas fueled, does not employ flame combustion, does not require electrical energy, and does not require external venting.

Other objects of the invention will in part be obvious and will in part appear hereinafter.

For a fuller understanding of the nature and objects of the invention, reference should be had to the following detailed description taken in connection with the accompanying drawings, in which:

FIG. 1 is a perspective view of a catalytic fluid heater exemplary of the invention;

FIG. 2 is a sectional view taken along lines 2-2 of FIG. 1; and

FIG. 3 is a sectional view taken along lines 3-3 of FIG. 2.

Similar reference characters refer to similar parts throughout the several views of the drawings.

Referring now to the drawings, a catalytic fluid heater l exemplary of the invention is shown and can be seen to be formed of a housing which can be a tall cylindrical tube 11, as illustrated. Housing of other shapes can be used, provided they provide a chimney effect, for reasons described more fully below. The housing may be of any common, noncorroding metal. The exterior of the housing 11 preferably is covered with an insulation material 12, from its top to a point just above a number of air ports 14 formed in it, in spaced positions about its periphery.

lnteriorly of the tubing 11, a gas diffusion plate 16 which may be a pressed stainless steel wool diffusion plate, is located just below the combustion air ports 14. Spaced above the air ports 14 is a metallic tube 18 which may be copper or other heat conducting metals such as aluminum or steel and which, as in the illustrated embodiment, may be formed into a series of concentric helical coils. A number (8 as illustrated) of perforated aluminum plates 20 are supported by the helical coils of the metallic tube 18 in various symmetric locations along the vertical axis of the tubing 1 1. Other configurations of the tube 18 also can be used, provided they support the plates 20 and function in the manner described below.

A catalyst is applied only to the lower surface of the perforated aluminum plates 20, so that combustion only takes place on the bottom surfaces of the plates, for reasons described more fully below. This catalyst preferably is applied in the manner disclosed in copending application, Ser. No. 443,128 filed Feb. 15, 1974, now abandoned, entitled A Catalytic Fluid Heater, and is of a type to combust hydrogen or other gases which are rich in hydrogen such as reformed natural gas and manufactured gas, in a flameless fashion.

As illustrated, a fluid such as water is caused to flow through the metallic tubing 18. The cold water enters the tubing 18 at its inlet 19, is heated as described below, and exits as hot water at the outlet 17. The water is coupled to and from the heater 10 in a conventional manner.

In operation, fuel is coupled to the heater 10, and enters at the bottom through the inlet 24. The fuel passes upwardly through the diffusion plate 16 located just below the combustion air ports 14 and is mixed with air drawn in through the combustion air ports 14. The combustible fuel-air mixture passes upward through the multi-layered catalyst beds formed by the perforated aluminum plates 20, and is combusted by the catalyst on these plates. The warm combustion products rising through the housing or tube 1 1 draws more air in through the ports 14, due to the chimney effect. The catalyst is of a type that will satisfactorily combust such mixtures of fuel (i.e., hydrogen, reformed natural gas, or low carbon monoxide content manufactured gas) and air with a sufliciently high flow rate as to maintain a chimney effect and combust enough fuel as to satisfactorily heat the fluid in the metallic tubing 18. Such catalysts can be of a noble metal type (platinum, platinum-rhodium, platinum-ruthenium, palladium, etc.) or of the noble metal oxide catalyst group.

The fluid (water) to be heated flows through the metallic tubing 18. The catalyst surface on the perforated aluminum plates is cooled by this fluid which is to be heated, and by the condensate formed on the copper tubing which is the product from the combustion of hydrogen in the fuel. These two cooling media maintain catalyst surface temperatures that are well below the auto ignition temperature of hydrogen. These low temperatures also only allow negligible concentrations of oxides of nitrogen to form.

The condensate formed on the copper tubing 18 also will fall from the lower portion of the helical coils and will pass through the diffusion plate 16 into a water trap 30 located at the bottom of the tubing 11. This water trap 30 allows the collection of pure water which may be drained from the heater 10 via the outlet tubing 32.

The fluid heater design depends on the thermal properties and flow rates of the fluid, the required fluid temperature rise, the catalyst activity, the fuel gas composition, and the coil configuration and number of catalyst plates that are desired. The capacity of a given heater can be increased by adding more catalyst plates. It has been found that catalyst plates Vs to A inch thick are satisfactory with approximately 20 percent open area (for combusting reformed natural gas on platinumcatalyzed anodized aluminum).

Generally, the taller the unit, the greater the chimney effect. This allows more air to be pulled through the combustion chamber. For every unit of cross sectional area of chimney tube, at least 3 units of catalyst surface should be used. The specific maximum combustion rate for complete combustion of reformed natural gas utilizing natural draft convection in this geometry fluid heater and using platinum-catalyzed aluminum is about 30,000 Btu/hr.ft This rate could be increased by using pure hydrogen gas fuel or by using a more active catalyst. Above this fuel gas flow rate, uncombusted hydrogen begins to escape from the heater; however, below this rate the units exhibit better than 99 percent complete combustion (with infinite turn-down control). The fuel gas flow can be moderated (proportionately controlled) or controlled in an on-off mode to meet heating demand.

A specific example of the fluid heater is a household water heating appliance which optionally humidifies the home (during cold or dry periods) or produces distilled quality water (during warm or humid periods). A small, 4 inches diameter engineering model has been constructed and tested for proof of concept. At a throughput of 8 gallons per hour (continuous flow of water), it requires a reformed gas feed rate of 7000 Btu per hour of about 27 cubic feet per hour (the reformed gas is 78% H 20.5% C 1% CH and 0.5% CO, with a high heating value of 260 Btu per cubic foot). The temperature rise in the water going through the unit is 80F (60F in, [40F out). Based on the high heating value of the fuel gas, the unit is 73 percent thermally efficient. Before steam condensation, the warm flue gas l50180F) contains essentially air, steam, and nitrogen. The levels of carbon monoxide and oxides of nitrogen are negligible and essentially the same as ambient room air.

For the 4 inches diameter engineering model the design parameters below were observed.

Catalyst surface Tubing Chimney height Accordingly, from'the above description, it can be seen that a catalystic fluid heater which is flameless and is fueled by hydrogen or other gases which are rich in hydrogen is provided. The fuel is combusted on the lower surface of the perforated aluminum plates to which the catalyst material is applied and will heat the fluid in the copper tubing. The fluid in the copper tubing 18 and the condensate formed on the copper tubing 18 which is the product from the combustion of hydrogen cools the catalyst surface so as to maintain the catalyst surface temperatures well below the auto ignition temperature of hydrogen, so that flame-type combustion is not implemented. The catalystic fluid heater therefore can be used without the need of external venting, thus special building construction to accommodate a chimney is not required.

Low flue temperatures in the neighborhood of 200F are maintained. Heat is transferred to the fluid to be heated by convection from the rising gases and by conduction from the catalyst supports, i.e., the perforated aluminum plates 20, that are in contact with the metallic tubing 18. The flue products will readily disburse and venting will be unnecessary, since the products of combustion will be steam only. With such low flue temperatures, efficiencies approaching percent can be obtained. The insulation is placed on the outside of the tubing 1 1 to allow for minimal radial heat losses and to enhance the chimney effect of the heater 10.

It will thus be seen that the objects set forth above, among those made apparent from the preceding description, are efficiently attained and certain changes may be made in the above construction. Accordingly, it is intended that all matter contained in the above description or shown in the accompanying drawings shall be interpreted as illustrative and not in a limiting sense.

Now that the invention has been described, what is claimed as new and desired to be secured by letters patent is:

l. A catalytic fluid heater which is fueled with a hydrogen-rich gas and of a construction which requires no external venting comprising:

a. a housing forming a combustion chamber open at the top end thereof and having orifice means for delivering said fuel into said housing at the lower end thereof, said housing further having an inlet means disposed above said orifice means for permitting air to flow into said housing for mixing with said fuel and being of a height to create a chimney effect to pull the air-fuel mixture through said housing from the lower to the top end thereof;

b. a tubing through which a fluid to be heated flows formed and vertically supported within said housing;

c. a plurality of plates supported by said tubing in various symmetric locations along the vertical axis of said tubing, said plurality of plates having a catalyst active with said hydrogen-rich gas applied to the lower surfaces thereof;

d. said fuel-air mixture in flowing upwardly through said housing impinging on said catalyst and being thereby combusted and producing condensate as a combustion product;

e. the combustion of said fuel-air mixture heating said plurality of plates and the fluid flowing through said tubing being heated both by convection from the rising gases and by conduction from said plurality of plates;

f. said plurality of plates being cooled by the fluid flowing through said tubing and said condensate such as to maintain the temperature of said catalyst below the auto ignition temperature of hydrogen whereby a flameless combustion of said fuel-air mixture results and negligible concentrations of oxides of nitrogen are formed, thus eliminating the need for external venting to an outside atmosphere.

2. The catalytic fluid heater of claim 1, wherein the fuel supplied thereto comprises hydrogen.

3. The catalytic fluid heater of claim 1, wherein the fuel supplied thereto comprises reformed natural gas.

4. The catalytic fluid heater of claim 1, wherein the fuel supplied thereto comprises low carbon monoxide content manufactured gas. 

1. A CATALYIC FLUID HEATER WHICH IS FUELED WITH A HYDROGENRICH GAS AND OF A CONSTRUCTION WHICH REQUIRES NO EXTERNAL VENTING COMPRISING: A. A HOUSING FORMING A COMBUSTION CHAMBER OPEN AT THE TOP END THEREOF AND HAVING ORIFICE MEANS FOR DELIVERING SAID FUEL INTO SAID HOUSING AT THE LOWER END THEREOF, SAID HOUSING FURTHER HAVING AN INLET MANS DISPOSED ABOVE SAID ORIFICE MEANS FOR PERMITTING AIR TO FLOW INTO SAID HOUSING FOR MIXING WITH SAID FUEL AND BEING OF A HEIGHT TO CREATE A CHIMNEY EFFECT TO PULL THE AIR-FUEL MIXTURE THROUGH SAID HOUSING FROM THE LOWER TO THE TOP END THEREOF: B. A TUBING THROUGH WHICH A FLUID TO BE HEATED FLOWS FORMED AND VERTICALLY SUPPORTED WITHIN SAID HOUSING, C. A PLURALITY OF PLATES SUPPORTED BY SAID TUBING IN VARIOUS SYMMETRIC LOCATIONS ALONG THE VERTICAL AXIS OF SAID TUBING, SAID PLURALITY OF PLATES HAVING A CATALYST ACTIVE WITH SAID HYDROGEN-RICH GAS APPLIED TO THE LOWER SURFACES THEREOF, D. SAID FUEL-AIR MIXTURE IN FLOWING UPWARDLY THROUGH SAID HOUSING IMPINGING ON SAID CATALYST AND BEING THEREBY COMBUSTED AND PRODUCING CONDENSATE AS A COMBUSTION PRODUCT, E. THE COMBUSTION OF SAID FUEL-AIR MIXTURE HEATING SAID PULRALITY OF PLATES AND THE FLUID FLOWING THROUGH SAID TUBING
 2. The catalytic fluid heater of claim 1, wherein the fuel supplied thereto comprises hydrogen.
 3. The catalytic fluid heater of claim 1, wherein the fuel supplied thereto comprises reformed natural gas.
 4. The catalytic fluid heater of claim 1, wherein the fuel supplied thereto comprises low carbon monoxide content manufactured gas. 